Silica sandstones vary in color and vary with the composition of the mixture. Siltstone is formed in an environment that has been transported over long distances, with relatively quiet hydrodynamic conditions and slow deposition rates. It can be graded into sandstone or clay rock in the lateral and longitudinal directions and constitutes a rhythmic bedding. Siltstone is formed under weak hydrodynamic conditions and often accumulates in lagoons, lakes, swamps, floodplains, deltas and sea basins.
Layered rocks may have been weathered for thousands of years and are visible to the naked eye. These layers are composed of various materials and minerals including silica, iron oxide, calcite, chlorite, quartz, feldspar, alumina, and potassium carbonate. The color of the rock formed by minerals, usually black, sand brown or gray. Although rocks are found all over the world, siltstones are only found in forests or in tropical regions, and usually siltstones are found in coal mine roadways.
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